Color digital video displays such as, e.g., flat-panel televisions, liquid crystal display (LCD) monitors for computer systems, and the like represent full color images by mixing of three basic colors: red, green and blue (RGB). The human visual system predictably perceives the close juxtaposition of these three basic colors as one resultant color. This illusion is the basis for color image processing.
Computer-based graphics/video systems include a graphics controller (and/or a video processor) that mixes red, green, and blue colors by assigning an intensity value to each constituent color. In this document, the term video processor is used to refer generally to either a video processor or to a graphics controller. Generally, the working range of intensity values is from zero to an upper threshold. The intensity values are converted to voltages, which are applied to a light source and/or color filter. Thus, a zero intensity value assigned to a specific color results in the corresponding color being completely dark. By contrast, an intensity value set at the upper threshold results in the corresponding color being presented at maximum intensity (i.e., at 100%). Intensity values assigned to the constituent colors produce corresponding, but not necessarily proportional changes in actual displayed brightness for the corresponding color and, thus, corresponding changes in resulting perceived color.
The term “gamma function” is used to define the relationship between the input voltage and the output brightness of a display. The brightness of a display should be equal to a constant multiplied by the input voltage raised to the power of gamma. Gamma is a rational number between zero and infinity which is provided by a monitor's manufacturer and is based on measurements made by the manufacturer.
Displays such as, e.g., cathode ray tube (CRT) displays or liquid crystal (LCD) displays exhibit variations in the color response. In most cases, the variances in basic color points from one monitor to the next are only slight. However, even small variances can result in a viewer perceiving different colors.
Presently, sRGB (standard Red Green Blue) monitors have the ability to precisely control intensities and, thus, the ability to display accurate colors. Many sRGB monitors are designed to utilize a standard non-linear color space that is reliably consistent across the various models of sRGB monitors. However, sRGB monitors are notoriously difficult to manufacture.
Manufacturers of electronic devices such as, e.g., displays, LCD televisions, and computer systems have implemented color correction techniques to correct color deviations in displays. Some color correction techniques utilize a color correction table which stores adjustment factors to be applied to intensity values. Examples of color correction techniques are presented in commonly assigned U.S. Pat. Nos. 6,862,029; 6,992,682; 7,046,255; and 7,106,344 to D'Souza et al., the disclosures of which are incorporated herein by reference in their entirety.
In some video displays the graphics processor (and/or video controller) may be designed by a first entity using a proprietary color table and the timing controller may be designed by a second entity also using a proprietary color table. The use of two different color tables increases the cost of the display, increases the computational complexity required for graphics processing, and may also result in sub-optimal color presentation.